France’s Socialist government has opened an investigation into claims women are being charged more than men for a range of products and services including razors, haircuts and dry cleaning.

The move was triggered by an online petition posted by a women’s rights group that claimed women were being systematically targeted by a hidden “pink” – or “woman” – tax.

The group is known as Georgette Sand, a play on 19th century French author George Sand, who famously used a male pen name in order to sell her novels.

Taking snapshots of products marketed for men and women, the group singled out Monoprix, a supermarket whose name translates as “one price”, as a particular offender.

In one case, Georgette Sand said women paid an extra eight euro cents for a packet of Monoprix’s standard razors, and got half as many razors as men.

Women, it said, are also being charged more than men for identical services at dry-cleaners and hairdressers.

While some differences in price may appear minimal, the group argued, they add up to an “unjustifiable injustice”.

It’s the economy, stupid

Georgette Sand’s petition rapidly garnered more than 20,000 signatures, prompting a response from the incriminated retailer.

In its defence, Monoprix claimed that “the larger sale, in volume, of men’s razors allows for a lower retail price”.

While this might make economic sense, it fails to explain why women’s cosmetics are not cheaper than men’s, even though it is safe to say – without wishing to sound sexist – that women on average buy more of them.

Monoprix also argued that women’s razors are more expensive to produce, without specifying why.

Finally, the French retailer offered two cases in which products marketed for men were more expensive than their female equivalents.

Georgette Sand was not impressed, immediately countering with an invitation to browse its "Woman Tax" Tumblr, which features dozens of pictures slamming cases of gendered pricing in French supermarkets.

These range from the obvious – women's deodorants costing more than similar products for men – to the more curious – washing-up gloves that are more expensive in small sizes (i.e. those more likely to be bought by women than by men).

Blame women

The row over gendered pricing seems to have caught the French unaware.

One marketing cabinet said it had "not yet had time to examine the issue".

Though largely new to France, the debate surfaced long ago across the Atlantic.

In 1996, California became the first US state to ban gendered pricing after finding that, on average, it cost women an extra $1,351 per year.

In a study published four years later, Consumer Reports asked manufacturers why their products for women were more expensive, and almost all said they cost more to produce – a premium women had apparently asked for.

One women’s body wash featured costlier technologies because “women told us they wanted a foaming action”.

Women’s perceived preferences also explained why one shaving foam can was “tall and thin rather than short and squatty", and cost more as a result.

In one case, the premium paid by women for pain relievers was simply the result of the retailer’s decision, the producer’s suggested price for men and women being the same.

Pink tax ‘made up’

According to Forbes magazine, import duties may also account for discrepancies in prices.

When lawyer Michael Cone dug into US tariffs, he found that women were on average subject to higher taxes on clothing imports.

In response, he gathered 100 companies and filed a lawsuit, which has been dismissed by several courts on the grounds that it failed to prove an intent to discriminate.

Whether French companies are prepared to do likewise is far from certain.

L’Oréal boss Jean-Paul Agon, who heads the world’s largest cosmetics company, has said he is “not at all aware of a pink tax”, a notion that “makes no sense” to him.

“I get the impression we are again making up something that doesn’t exist”, he told reporters on Monday.

France's Finance Ministry has vowed to take action should its inquiry reveal a practice of unfair pricing.

In the meantime, women have had to swallow another bitter pill.

As Georgette Sand pointed out, until 2012 female drivers in Europe enjoyed cheaper car insurance policies on the grounds that they accounted for a fraction of road accidents.

But the European Union has since ruled that this discriminated against men.